Carriers keep shrinking the size of seats in order to stuff more people into their planes.

Empty middle seats that might provide a little more room have vanished. And more travelers who have bought tickets are being turned away because flights are overbooked.

A report being released Monday says consumer complaints to the Transportation Department surged 20 percent last year even though airlines have been doing a better job by other measures, like on-time arrivals and mishandled baggage.

In recent years some airlines have shifted to larger planes that can carry more people, but that hasn't been enough to make up for an overall reduction in flights.